Common infusion packets utilize water-permeable bags of paper material to contain the percolative product, such as tea, coffee or herb particles. The porosity of the paper bag is selected to prevent the percolative product to sift-out of the water-diffusion apertures, while allowing the flavouring substance released in the steeping liquid to freely egress the infusion packet and disperse in the surrounding body of water.
Paper bags offer the advantage of being relatively inexpensive. In addition they can be sealed on high speed automatic equipment that enables to mass produce the infusion package at low cost. However, paper material has some drawbacks, such as a poor wet-strength that may cause the infusion packet to break open in use or otherwise undesirably dispel its contents. Furthermore, the paper material may not have a degree of water-permeability that is sufficiently high for an optimal percolation effect to take place.
Infusion packets have also been manufactured with bags of fibrous, non-woven material, as disclosed in the Canadian patent 802,720 granted to Johnson & Johnson, U.S.A. on Dec. 31, 1968. The subject matter of this patent is incorporated herein by reference. Bags of non-woven fibrous material present certain advantages over paper bags such as an increased wet strength and a higher water-permeability. However, bags of non-woven fibrous material are difficult to seal in a reliable fashion on conventional high-speed equipment primarily due to the fact that the bag walls must remain in contact with the heat-sealing dies for a comparatively long period of time which significantly reduces the overall production rate, thereby making the final product more expensive to manufacture.